In one type of shock absorber, a coiled length of tow rope is contained within an elastically extensible casing which expands and contracts in response to the amount of tension on the two rope. This type shock absorbing device does not have interchangeable parts and no provisions are made for water drainage and inspection of the component parts within the casing interior.
In another type of shock absorbing device a pair of concentric springs having different spring rates are contained within a casing which is in turn provided thereover with a buoyant envelope. In such a device the envelope must be removed to provide access to the component parts of the shock absorber. Whereas there are provided pressure release vents within the casing, there is no provision to permit venting and drainage through the buoyant envelope. In addition no positive gripping means are provided to facilitate assembly or disassembly of the device, for example, to incorporate interchangeable parts.